The objective of this proposal is two-fold: to construct a gene fusion between the ribosomal RNA promoter (rrnP) and some suitable, well characterized operon such as tryptophan (trp), and to use the rrnP-fusion to study various aspects of rRNA genetics and control. The desired gene fusion will be constructed in vitro using restriction endonucleases. The recent purification of restriction endonucleases and characterization of the DNA sequences they recognize has made possible the assembly of genetic information from a variety of sources in a highly controlled fashion. Cleavage of phage DNA containing either the rrn genes of the trp genes gives rise to unique DNA fragments. These fragments will be inserted into a self-replicating plasmid. These plasmids will then be screened for the desired fusion. The rrnP fusions identified will be used to study rRNA genetics and control, such as the mechanism of rRNA transcription initiation and control. The fusions will also be used to select mutants at rRNA control sites which will subsequently be studied both in vivo and in vitro. The promoter fusions and these mutants will be used to locate and determine the nucleotide sequences of the rrn operon control elements.